Cerebrospinal fluid outflow and intracranial pressure in hydrocephalic patients with external ventricular drainage

Abstract

Background and purpose: The aim of this study was to monitor the 24 h cerebrospinal fluid (CSF) outflow and intracranial pressure (ICP) in hydrocephalic adult patients with external ventricular drainage (EVD).

Patients and methods: Twelve patients (5M/7F) aged 30-69 years suffering from acute hydrocephalus requiring EVD were admitted in the neuro-intensive care unit. The CSF collecting bag was continuously weighted using a high-precision scale, the filtered output of which was fed at 1 Hz to a computer and converted to flow (Q'ext(csf)). ICP was also recorded.

Results: One patient was excluded because more than 80% of the Q'ext(csf) data were rejected by the system. The mean +/- SD Q'ext(csf) and ICP were respectively 7.5 +/- 3.4 ml/h (range 1.6-12.1 ml/h) and 12.4 +/- 2.7 mmHg. Two patterns of Q'ext(csf) were identified: a continuous profile and a discontinuous one with numerous bursts frequently associated with manoeuvres such as cough or chest physiotherapy. The short-term variations of Q'ext(csf) and ICP were usually unrelated.

Conclusion: The study stresses the important inter and intra-subject variability of Q'ext(csf) in patients with EVD. The mean Q'ext(csf) is lower than the reference production rate (21 ml/h), raising the question of persistent CSF absorption and/or depressed secretion. The independent changes of Q'ext(csf) and ICP on the short term is likely to be explained by the pressure-volume characteristics of the intracranial space.